Exciton-Polaritons with Size-Tunable Coupling Strengths in Self-Assembled Organic
Microresonators
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Abstract
Self-assembled nano/microcrystals
of organic semiconductors with
regular faces can serve as optical microresonators, which hold a promise
for studying the light confinement and the light-matter interaction.
Here, single crystalline microribbons of 1,4-bis(2-(4-(<i>N</i>,<i>N</i>-di(<i>p</i>-tolyl)amino)phenyl)-vinylbenzene
(DPAVB) are synthesized with well-controlled sizes by a facile solution-exchange
method. We find that individual microribbon can work as Fabry-Pérot
(FP) resonator along its width (<i>w</i>), in which strong
coupling of optical modes with excitons results in the formation of
exciton polaritons (EPs). The dispersion relation of <i>E</i> ∼ <i>k</i><sub><i>z</i></sub> of EPs
is constructed by extracting the energies (<i>E</i>) of
FP resonances at integer multiples of π/<i>w</i> in
the wavevector (<i>k</i><sub><i>z</i></sub>) space.
By simulating the significantly curved dispersion of EPs with a two
coupled harmonic oscillator model, a coupling strength between 0.48
and 1.09 eV are obtained. Two coupling regimes are classified: in
regime I, the coupling strength is constant at 0.48 eV for microribbons
with the cavity length of <i>w</i> ≥ 2.00 μm;
in regime II, the coupling strength increases dramatically from 0.48
to about 1 eV with decreasing the resonator length from <i>w</i> = 2.00 to 0.83 μm. More significantly, our results suggest
that the exciton-photon coupling strength could be modulated by varying
the size of microribbon cavities, providing an effective method for
engineering the light–matter interaction in organic single
crystalline microstructures